Method of preserving ice nuclei for snow formation

ABSTRACT

A nozzle having first and second axially aligned orifices spaced apart. An annular disc-like chamber is disposed between and surrounds the orifices. A carrier fluid, such as compressed air, is discharged from the first orifice, through the chamber and from the second orifice which results in an airstream containing ice nuclei. A liquid, such as water, flows through the chamber in thin-film form and into the carrier fluid flowing through the chamber. The liquid then flows across the peripheral edge of the second orifice and is broken up into droplets of substantially uniform size which are dispersed in the airstream.

United States Patent Howell 1 Nov. 27, 1973 [54] METHOD OF PRESERVING ICE NUCLEI 3,163,329 12/1964 Mornas 239/434 X FOR SNOW FORMATION 3,464,625 9/1969 Carlsson 239/2 S Inventor: Wallace E. Howell, Lexington, Mass.

Assignee: Hedco, lnc., Bedford, Mass.

Filed: Aug. 14, 1972 Appl. No.: 280,237

Related US. Application Data Division of Ser. No. 131,320, April 5, 1971,

abandoned.

References Cited UNITED STATES PATENTS l/l939 Pontius, Jr. 239/434 X Struble et a1. 239/2 S UX 4/1954 Pierce, Jr. 239/434 X COMPRESSED MOIST AIR.

Primary Examiner-M. Henson Wood, Jr. Assistant Examiner.lohn J. Love Att0rneyRichard L. Stevens et al.

57 ABSTRACT A nozzle having first and second axially aligned orifices spaced apart. An annular disc-like chamber is disposed between and surrounds the orifices. A carrier fluid, such as compressed air, is discharged from the first orifice, through the chamber and from the second orifice which results in an airstream containing ice nuclei. A liquid, such as water, flows through the chamber in-thin-film form and into the carrier fluid flowing through the chamber. The liquid then flows across the peripheral edge of the second orifice and is broken up into droplets of substantially uniform size which are dispersed in the airstream.

6 Claims, 3 Drawing Figures PATENTEUNHVZ? I975 3.774.842

COMPRESSED MOIST AIR H2O P FIG. 2

l E g g 22 COMPRESSED FIG. 3

MOIST AIR L L INVENTOR WALLACE E. HOWELL 2 ATTORNEYS BACKGROUND OF THE INVENTION In 1946, Langmuir and Schaefer demonstrated the use of very large numbers of minute ice nuclei to convert clouds of supercooled water droplets to snow. They accomplished the production of ice nuclei originally by dropping pulverized dry ice into the cloud; the dry ice chilled the film of air coming in contact with it to a temperature below 40, the self-nucleating temperature for water, and induced the formation of large numbers of ice nuclei directly from the vapor state. Inside the cloud, where the pressure was in equilibrium with liquid water, these ice nuclei grew rapidly and became small snow flakes. Subsequently, in 1947, Vonnegut demonstrated that sudden adiabatic expansion of compressed moist air also produced ice nuclei in large numbers by driving the temperature momentarily below 40. His method was to seal compressed moist air into'a small glass ampoule which was .then placed in a cold chamber filled with supercooled cloud and ruptured, allowing sudden expansion of the released air.

In the art of snowmaking, ithas proven desirable to separate the process of breaking up water into a fine spray and mixing it with the atmospheric air from the process of producing ice nuclei to infect the water droplets when they become super-cooled, accomplishing these two-operations in separate zones of the snowmaking apparatus, see for example US. Ser. No. 854,103, nw U.S..Patents 3,703,991 and 3,733,029 which application is hereby incorporated into this application in its entirety. However, when this isdone, the ice nuclei are exposed to mixture with air having a vapor pressure lower than equilibrium with ice, before this air becomes mixed with the water spray; and during the interval between their, formation and their mixture with the water spray, the ice nuc i. su fer oss by ap a i n qthisslrxair- In order for them to become effective, it is necessary toprovide protection for these nuclei against evaporation. This loss through evaporation may be partially controlled by providing an environment of high humidity about the ice nuclei. This was primarily accomplished by flowing a moist airstream about the ice nuclei as set forth in US. Pat. No. 3,567,] 17.

SUMMARY OF THE'INVENTION My invention broadly provides a device wherein a first fluid, such as a carrier fluid, is discharged from a nozzle. The discharge of the nozzle is in communication with a chamber and' a second downstream orifice. A second fluid, such as a liquid, is introduced into the chamber and flows through the chamber in thin-film form. The carrier gas flowing through the chamber flows through the orifice with the liquid. The liquid, which is discharged with the carrier gas, flows into the carrier gas and across the peripheral edge of the orifice and is broken down into droplets of substantially uniform size. These droplets commingle or are dispersed within the carrier gas to provide moistening of the carrier gas, drying of the liquid, or simply complete dispersion of the droplets of substantially similar size in the carrier gas. I

In a preferred embodiment the carrier gas is compressed air containing a substantial amount of water vapor which upon discharge from the nozzle provides for the production of ice nuclei. Water as the second fluid is introduced into the chamber and is discharged in thin-film form. The airstream carrying the ice nuclei is discharged through the orifice. The water flowing across the orifice periphery is broken into minute water droplets which mix with the airstream carrying the ice nuclei. The water droplets then moisten the airstream by evaporation and hence raise the local vapor pressure above saturation with respect to the ice nuclei.

DESCRIPTION OF THE DRAWINGS FIG. 1 is a sectional view of the nozzle of the invention; and

FIGS. 2 and 3 are schematic illustrations of alternative embodiments of the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT(S)'- Referring to the figure of the drawing, a nozzle 10 includes a conical passage 12 in communication with a duct 14. The duct 14 communicates with a source of moist compressed air. A second passageway 16 as shown of smaller diameter than the duct 14 communicates with water under pressure and passes through the inside of the first duct. The front portion of the nozzle has a shoulder 20 and is threadedly engaged by a cap 22 which when fully engaged rests against the shoulder 20 in such a manner as to define the annular chamber 18. The cap has an annular knife edge 24 defining an orifice 26 therein spaced apart from and'axially aligned with the end of the nozzle. i

In the operation of my invention, water flows through the passageway 16, into the chamber 18 and'radially inward emerging into the airstream in the form of a is adiabatically expanded to form ice nuclei by spontaneous nucleation, which results in an airstream charged with ice nuclei. This airstream flowsthrough the chamber and is discharged from the orifice 26 carrying the water droplets with it. The ice nuclei are formed in and i emerged within the central part of the airstream while the water droplets substantially surround the central part. The air pressure for the moist compressed air may range between about 25 to 125 psi, say 40 psi, while the water pressure flowing through passageway 16 may range from 15 to psi, say for example 30 psi, but'in any instance at some pressure less than the air pressure of the compressed moist air through the duct 14. The depth of the chamber 18 may vary from 0.001 to 0.005 inches, say for example about 0.003 inches. The water droplets maintain a vapor pressure about the ice nuclei greater than the vapor pressure of the ice nuclei thereby inhibiting the evaporation of the ice nuclei. The droplets, rather than substantially surrounding" a centralairstream of ice nuclei, may be partially or comcharge end of the first passageway and the chamber 18, it is obvious that a plurality of passageways may be used for transporting the water under pressure or the second passageway may be concentric about the first duct.

In the formation of the ice nuclei there are a considerably greater number of ice nuclei formed than the amount of spray droplets, enough in fact to infect all of the droplets formed in the spray and then subsequently infect separately formed water droplets as described in US. Ser. No. 854,103. When the spray droplets are infected, they remain at about C until they become icelike or snow-like particles thus having a vapor pressure higher than that of the remaining ice nuclei which they preserve. The ambient of environmental air about the spray droplets and ice nuclei being less than 0C, the ice or snow-like particles continue to maintain a higher vapor pressure as they cool to the environmental air temperature. However, by this time the infection of the separately formed water droplets has been accomplished.

In the preferred embodiment the spray droplets are infected with ice nuclei and in fact substantially all of the spray droplets are infected. However, our invention operates equally as well even if only a portion of the spray droplets are infected or if none are infected as long as the vapor pressure of the droplets remains above that of the ice nuclei in order that the ice nuclei may be preserved until infection of the separately formed water droplets. Accordingly, it is seen that the nozzle per se can in its preferred embodiment form snow. However, the amount of snow formed as compared to the process described above does not maximize the efficiency which can be achieved in the preferred embodiment, its primary function being to preserve those ice nuclei which subsequently infect the separately formed water droplets.

In FIG. 2 is shown an alternative embodiment of the invention wherein a passageway 28 is concentrically aligned with the duct 14.

FIG. 3 is a simplified schematic of a further alternative embodiment wherein two passageways similar to 16 are introduced into the upper and lower portions of the nozzle as shown.

Although shown as a combination of a nozzle with a cap to define the chamber 18, it is of course within the scope of the invention that the chamber may be defined in other ways such as within or as a part of a unitary nozzle. It is preferred that the cap be threadingly engaged or otherwise engaged in a removable manner whereby the dimensions of the chamber may be varied depending upon processing requirements. The chamber has been shown as disc-like in the preferred embodiment of the invention which ensures that the water introduced into said chamber will flow toward the orifice 26 in a sheet-like or film-like form. However, other chamber structures may be employed to achieve the same result, such as tapered. Further, the liquid thin film has been shown in the preferred embodiment as flowing in a direction substantially normal to the flow of the carrier gas. If desired, the thin film may flow into the carrier gas in an annular direction. I

The annular knife edge is preferred, but any nonannular configuration, such as elliptical, semicircular, etc., may be used, and the knife edge may be nonuniform, such as a serrated edge. A flat or other structural surface rather than a knife edged orifice may be employed depending upon the fluid which is being formed into droplets. The water does not have to be introduced between the outer peripheral edges of the chamber orifice and the nozzle, but. may be introduced into one end thereof as shown in FIG. 3, either alone or in combination with side introduction as shown in the lower portion of FIG. 3.

This invention differs in both form and function from a common form of air-liquid atomizer which consists of a small liquid jet controlled by a needle valve, this jet being surrounded by a second jet of air emerging through an annular opening in a direction parallel with the liquid jet. In a nozzle of this type, the drop size is determined mainly by the manner in which the jet of liquid breaks up into droplets, as the two jets move parallel to each other. Since the shearing action of the air jet is greatly diminished by the parallel velocity of the water drops, very small droplet sizes are not generally produced. A further drawback for the purpose of ice nucleus production is that the water is introduced into the central part of the air jet rather than into its periphery.

In my invention, the water emerges in a controlled thin film which breaks up into smaller droplets of more uniform size, thereby providing better protection for the ice nuclei. I

My invention in its broader aspect provides a nozzle for forming a spray of very small droplets of substantially uniform size, and in its preferred embodiment has been described in combination with the formation of a cone-type spray to protect ice nuclei from evaporating prior to infection of water droplets in a snow making .environment. Accordingly, any applications which include the dispersion of fluids, such as solutions and suspensions of various sorts for the purpose of drying materials, such as the evaporative drying of coffee to produce a coffee powder, and the dispersal of liquids into an airstream where massive and rapid moistening of the airstream is desired are within the scope of this invention. 7

Having described my invention, what I now claim is: l. A method for making snow, which comprises:

a. forming in a first zone waten droplets;

b. forming an ice nuclei and water droplet mixture in a second separate zone by:

i flowing a stream of moist compressed air through a conduit,

ii expanding adiabatically the compressed air to form ice nuclei by spontaneous nucleation,

iii contacting the compressed air stream with a thin film of water, whereby water droplets are formed having a vapor pressure higher than the vapor pressure of the ice nuclei,

iv commingling the water-droplets and ice nuclei to form the mixture of ice nuclei and water droplets to inhibit the evaporation of the ice nuclei;

c. maintaining the integrity of the mixture until the water droplets formed in the first separate zone are infected by the ice nuclei formed in the second zone whereby the infected droplets exchange their latent heat with the atmosphere and eventually become snow-like crystals.

2. The method of claim 1, which includes: dispersing completely the water droplets throughout the ice nuclei stream.

3. The method of claim 1, wherein the formation of the mixture includes:

discharging the ice nuclei in the central part of the mixture; and

the water in thin-film form in a direction substantially normal to the direction of flow of the compressed air.

6. The method of claim 1, wherein the water droplets in the water droplet mixture are of a substantially uniform size. 

1. A method for making snow, which comprises: a. forming in a first zone water droplets; b. forming an ice nuclei and water droplet mixture in a second separate zone by: i flowing a stream of moist compressed air through a conduit, ii expanding adiabatically the compressed air to form ice nuclei by spontaneous nucleation, iii contacting the compressed air stream with a thin film of water, whereby water droplets are formed having a vapor pressure higher than the vapor pressure of the ice nuclei, iv commingling the water droplets and ice nuclei to form the mixture of ice nuclei and water droplets to inhibit the evaporation of the ice nuclei; c. maintaining the integrity of the mixture until the water droplets formed in the first separate zone are infected by the ice nuclei formed in the second zone whereby the infected droplets exchange their latent heat with the atmosphere and eventually become snow-like crystals.
 2. The method of claim 1, which includes: dispersing completely the water droplets throughout the ice nuclei stream.
 3. The method of claim 1, wherein the formation of the mixture includes: discharging the ice nuclei in the central part of the mixture; and surrounding the central part of ice nuclei by the water droplets.
 4. The method of claim 3, wherein the water droplets of the water droplet mixture are substantially uniform in size.
 5. The method of claim 1, which includes: flowing the water in thin-film form in a direction substantially normal to the direction of flow of the compressed air.
 6. The method of claim 1, wherein the water droplets in the water droplet mixture are of a substantially uniform size. 